1. Field of the Invention
This invention relates to pavement working machines, and more particularly to an apparatus for removing sealant materials from the expansion joints between pavement slabs prior to replacement of the sealant.
2. Description of the Prior Art
It has long been known that concrete slabs used for paving roadways, aircraft landing strips, the floors of buildings, and the like, must be provided with expansion joints at spaced intervals to allow expansion and contraction of the slabs resulting from ambient temperature deviations. Such expansion joints may be formed by the casting thereof simultaneously with pouring of the cement slabs, or may be cut therein after curing of the cement. Typically, such joints will be formed at about 25 foot intervals, will be about one to one and a half inches deep and will vary in width from three-eights of an inch to about one and one-half inches. These dimensions however, are only typical in that they may vary considerably.
In addition to expansion joints being used between adjacent slabs of concrete, expansion joints are often needed in other types of pavement. For example, a paved surface consisting of a concrete slab having an adjacent asphalt surface such as a concrete roadway having an asphalt shoulder strip. However, it is much more common that such joints are used in adjacent slabs of concrete, thus, the pavement will hereinafter be referred to as concrete.
It is also well known that the above described expansion joints must be filled with an elastomeric sealant to prevent the entry of foreign materials. If water is allowed to enter and pass downwardly through expansion joints, the concrete supporting bed may be washed away which can result in settling or cave-in of the cement slabs. If water is trapped in expansion joints during freezing weather, repturing of the concrete slabs can result. If noncompressible materials such as sand or dirt enter into the expansion joints, slab rupturing can occur upon expansion of the slab due to relatively warm ambient temperatures.
Various types of joint sealing materials have been used such as rubberized asphalt, coal tar extended polysulfide, polyurethane polymers, rubberized polyvinyl chloride, and the like. However, thermal expansion and contraction, exposure to the elements, spillage of gasoline and solvents and heavy loading of the concrete slabs will cause a gradual breakdown in the sealants which must be periodically removed and replaced to prevent damage to the concrete surface. The time interval between the necessary replacement of the sealants depends upon the nature of the sealants and the conditions to which it may be exposed. Some sealants will need to be replaced at intervals as short as two or three years, while others in less demanding environments will last up to ten years or more.
Regardless of the type of sealant used in an expansion joint and the environment, sealants must be periodically removed and replaced with the task of sealant removal being difficult and time consuming.
The most widely used type of apparatus for removing old sealants from expansion joints consists basically of an arm extending rearwardly from a suitable motorized vehicle such as a tractor. The arm is raised and lowered such as by hydraulics which are controlled from the vehicle and the arm is provided with a joint cleaning tool at its trailing end. The joint cleaning tool is lowered hydraulically, or otherwise, into the joint to be cleaned so that forward movement of the towing vehicle will pry or scrape the old sealant out of the joint. Examples of this basic type of prior art structure are fully set forth in U.S. Pat. Nos. 2,541,309, 2,584,993 and 3,043,200, and numerous problems have been encountered in connection with such mechanisms.
Removal of the old sealants from expansion joints in concrete slabs is very difficult due to the inherent nature of the material itself in that prying alone will leave a sealant residue on the side walls of the expansion joint, and proper bonding of the new sealant cannot be achieved. To overcome the sealant residue problem, the use of abrasive wheels, diamond saws and sand blasting all have been employed subsequent to prying the sealant out of the expansion joint. Such subsequent operations did not prove economically feasible in that they necessitated the transporting and use of additional equipment and manpower, thus the operational costs and time involved proved to be prohibitive.
Therefore, the above described prying and subsequent cleanup operations have, for the most part, been replaced with a single scraping or cutting operation in which the walls of the expansion joint are forcefully scraped so that a relatively thin layer of the concrete itself is cut away simultaneously with the removal of the old sealant. Such a single scraping, or cutting, operation will expose a clean residue free surface within the expansion joint so that proper bonding of the replacement sealant is easily accomplished. However, the single scraping or cutting operation requires that considerably larger forces be applied, as compared to the prying operation, and the prior art devices such as those disclosed in the above referenced U.S. patents were not designed for such use.
Another problem with these prior art devices was the difficulty experienced in keeping the joint cleaning tool, or bit, in the expansion joint as the towing vehicle moves along the joint. This tracking problem will be appreciated upon consideration that expansion joints, especially those that are cut after the concrete slab has cured, are not always perfectly linear, and it is extremely difficult to drive the motorized vehicle in a path that is perfectly straight and coincident with the expansion joint. For this reason, the above described prior art mechanisms employed some form of a pivot or swivel joint at the forward end of their trailing arms. With the rearwardly extending arm being capable of pivotable movement the arcuate path in which the joint cleaning tool bit was free to move was adequate as long as a prying type of operation was being employed, however, such movement of the tool bit in an arcuate path transverse to the expansion joint proved to be troublesome when the single scraping, or cutting, technique was employed. In removing the old sealant by a scraping or cutting operation, the joint cleaning tool bit must be provided with concrete cutting edges on opposite sides of the bit, and if the bit is allowed to assume a skewed attitude in the expansion joint as a result of pivotal movement of the trailing arm, unbalanced cutting forces will be applied. If the skewed position of the tooling bit is severe enough, one or the other of the concrete cutting edges may miss the side wall entirely and the bit will tend to crawl up the engaged side wall of the joint being cleaned and pull itself out of that joint.
In an attempt to overcome some of the above described problems, an improved expansion joint cleaning mechanism was devised and that mechanism is fully disclosed in U.S. Pat. No. 3,791,696. Briefly, this specific prior art mechanism includes a substantially square frame upon which a pantograph-like swing arm is carried, with the swing arm having a joint cleaning tool bit on the trailing end thereof. The pantograph-like swing arm includes two pair of spaced apart upper and lower plates which are pivotably connected to the forward crossbar of the frame and extend rearwardly therefrom in cantilever fashion so as to straddlingly pass above and below the rear cross member of the frame. A bar is pivotably connected between the rearwardly disposed ends of the plates and a tool holder, for mounting of the tool bit, is carried on the bar. The frame is pivotably coupled at its forward end to the rear of the motorized vehicle so as to be pivotably movable about a horizontal axis. This pivot movement, which is employed to raise and lower the trailing edge of the mechanism relative to the joint, is accomplished by means of a hydraulic cylinder that is connected between the vehicle and the frame. This pivot movement of the frame is transmitted through the rear crossbar of the frame to the swing arm plates, so that the swing arm will forcefully hold the tool bit in the joint being cleaned.
This briefly described specific prior art joint cleaning mechanism is a substantial improvement over preceding mechanisms; however, some problems still exist. In the first place, the hydraulic cylinder employed to move the device is connected to one of the corners of the frame which is at the forward end of the frame adjacent the pivot connection thereof to the vehicle. Connection of the hydraulic cylinder at that point of the frame is inherently poor design in that the downwardly applied force necessary to hold the tool bit in the joint is at the opposite end of the frame and is applied in an off-center position. Thus, the frame must be very heavy structurally, so that deflection and twisting forces will not distort the frame. Secondly, although the pantograph-like swing arm will maintain the desired nonskewed position of the tool bit in the expansion joint, the swing arm will inherently try to straighten itself into a perfect square, or rectangle, when being pulled by the vehicle. This tendency for self-straightening of the swing arm, coupled with the fact the pulling forces exerted by the vehicle can, and very often are, being applied at an angle relative to the path of the expansion joint, i.e., not coincident therewith, results in uneven application of the pulling forces and results in an unbalanced cutting pressure being applied to the side walls of the expansion joint. In the event that the angular relationship between the pulling forces applied by the vehicle, and the path of the joint becomes excessively large, gouging and chipping of the side walls of the joint may result, and in some instances, the tool bit may be pulled completely out of the joint.
Therefore, a need exists for a new and improved mechanism for removing old sealant material from the expansion joints between concrete slabs with the new and improved mechanism overcoming some of the problems and shortcomings of the prior art.